1. Field of the Invention
The present invention relates to a transfer sheet employable as color proof for use in color proofing or display, and more particularly relates to a photosensitive image receiving sheet material suitable for use in an image forming process which comprises transferring a transferable image formed on a temporary support to an image receiving sheet material and then re-transferring said image to a permanent support.
2. Description of prior art
There is known an image transfer process which comprises exposing a photosensitive laminate composed of a peelable layer consisting of an organic polymer and a photosensitive resin layer provided on a temporary support to light, developing it to form an image on the peelable layer and transferring the image onto a given support (i.e., permanent support) by using an adhesive (see, Japanese Patent Publication No. 46(1971)-15326 and No. 49(1974)-441). This process had advantages in that it can be used as color proof for various procedure such as of overlay type, surprint type, etc. However, that process has disadvantages in that an adhesive has to be used for every transferring operation and hence the process is complicated and in that there is a difficulty in keeping the accuracy of registration in transferring each color.
To eliminate the complication of the process, there are proposed processes wherein after the formation of an image, the image is laminated to a permanent support under the application of heat and pressure (see, Japanese Patent Provisional Publications No. 47(1972)-41830, No. 48(1973)-9337 and No. 51(1976)-5101). Particularly, Japanese Patent Provisional Publication No. 51(1976)-5101 discloses that a hot-melt polymer layer as an adhesive is provided on a permanent support and Japanese Patent Provisional Publication No. 47(1972)-41830 discloses that an image is laminated directly to a permanent support such as art paper or coated paper.
However, these processes still have various disadvantages in that the final image is laminated to a permanent support in such a manner that the right and the left are reversed against the original image and in that when a hot-melt polymer is used as an adhesive, the melting point thereof is usually high and hence the transferring temperature has to be high so that the dimensional stability of the support is lowered by the influence of heat, and the deviation of colors from one another in registration is caused in transferring each color. When a hot-melt polymer having a low melting point is used as an adhesive, there are the problems that after the formation of an image, sticking is caused, or the surface thereof is liable to be marred.
As a process for eliminating the above-described disadvantages, there is proposed in Japanese Patent Provisional Publication No. 59(1984)-97140 a process wherein an image is laminated to a temporary image receiving sheet before the image is laminated onto a permanent support. This process includes steps of: preparing a temporary image receiving sheet provided with an image receiving layer composed of a photopolymerizable material on a support; transferring an image of each color onto the temporary image receiving sheet before the image of each color is laminated to a permanent support; re-transferring said image onto a permanent support; and exposing wholly it to light to cure the laminated photopolymerizable image-receiving layer.
The above-described image transferring process using the temporary image receiving sheet (hereinafter referred to simply as image receiving sheet) is very effective in eliminating the aforementioned problems. In more detail, there are the following advantages. An erect image corresponding to the masked original image can be formed on the permanent support. Since an ethylenically unsaturated polyfunctional monomer serving as a photopolymerizable substance is incorporated in the photopolymerizable image receiving layer of the image receiving sheet, the photopolymerizable image-receiving layer itself is soft, transferring can be carried out at a low temperature and after transferring, it can be exposed wholly to light to cure it. In more detail, there are the advantages that after the transfer of the image, sticking is not caused and the final image has high resistance to marring.
In the image receiving sheet employed in the process of the Japanese Patent Provisional Publication No. 59(1984)-97140, adhesion betweeen the photopolymerizable image receiving layer (that is, photopolymerizable adhesive layer) and the support is very high in the unexposed state. Therefore, when the photopolymerizable adhesive layer having a received image is laminated to the final support and the support for the image receiving material is peeled off before the exposure operation, peel marks (that is, linear crack produced on the photopolymerizable adhesive layer due to excessive shock brought about by the peeling operation, or stain given by a portion of the adhesive layer remaining on the surface of the image-receiving layer) are liable to be formed on the surface of the laminated image-containing photopolymerizable adhesive layer. Hence, in the process of the Japanese Patent Provisional Publication No. 59(1984)-97140, the image-containing photopolymerizable adhesive layer is laminated to the final support and the whole is exposed to light to cure the photopolymerizable adhesive layer. At the same time, adhesion between the photopolymerizable adhesive layer and the support of the image receiving sheet is lowered and the support is removed.
Though the above-described image transferring process is effective in obtaining the final image of high quality, the present inventors have found that said process should be improved on the following problems.
When a support having high surface smoothness is used as a support for the image receiving sheet in said image transferring process using an image receiving sheet, the surface of the final image laminated to a permanent support is glossy. On the other hand, when a color proof for color proofing is to be prepared utilizing the image transferring process, it is necessary that the surface of the color proof is roughened to allow it to approximate to the surface of a print. Roughening is generally performed using a process wherein an appropriate mat film is laminated on the surface of the final image and then the surface of the image is matted by heating under pressure.
In order to mat the surface of the final image formed on the permanent support by the process stated in the Japanese Patent Provisional Publication No. 59(1984)-97140, a mat film is placed on the cured (i.e., hardened) adhesive layer, and heat and pressure must be applied to the surface. High heat and high pressure are required for the matting of the surface of the image, and the final image is liable to suffer deterioration under such severe conditions.
In other problems, when a photosensitive material which is a positive type and release nitrogen gas during photolysis such as naphthoquinone diazide is used in the transferable photosensitive image forming material, naphthoquinone diazide is decomposed and nitrogen gas is released in curing the photopolymerizable adhesive layer by light exposure. Nitrogen gas stays at the interface between the image part and the cured adhesive layer. Thus, when a subsequent high-temperature matting treatment is carried out, the interface is deformed by expansion of the nitrogen gas and the quality of the image is deteriorated.
In summary, it is desirable that the matting of the surface of the image is carried out in such a manner that while the image receiving layer is still soft (that is, before the photopolymerizable material of the photopolymerizable image receiving layer together with image placed on the permanent support is cured), and an appropriate mat film is placed on the surface of the image and the surface of the image is matted by heating under pressure. However, there is a problem that peel marks are formed on the surface of the image receiving layer in removing the support for the image receiving sheet from the laminated photopolymerizable image receiving layer as described above.